mRNA translation in erythropoiesis

Project leader: Marieke von Lindern 

Role of mRNA translation in erythropoiesis

To produce peripheral blood erythrocytes in correct amounts, the proliferation of erythroid progenitors and their maturation to erythrocytes must be well balanced in the process of erythropoiesis. We are able to culture large numbers of erythroid progenitors from bone marrow or blood in presence of erythropoietin (Epo), stem cell factor (SCF) and glucocorticoids. If we transfer the cells to medium supplemented with Epo and insulin the cells differentiate towards erythrocytes. The cells become smaller and accumulate hemoglobin, the chromatin condenses and eventually the nucleus is expelled. 

The aim of the group is to understand how external factors control the balance between proliferation and maturation during erythropoiesis.

Whereas transcription factors lay out the basic gene expression program, a cell’s proteome is determined by many post-transcriptional processes among which is mRNA translation. We previously showed how growth factor signaling is required for the translation of transcripts with long 5’-untranslated regions (5’UTR) and a complex secondary structure. The 5’UTR of many transcripts that are subject to tight control of translation also contain small upstream open reading frames (uORFs). Such uORFs control the use of downstream translation start sites. For instance low iron availability, which may occur in donors that frequently donate blood, may affect the translation of these transcripts. To identify important mechanisms that control erythropoiesis in response to external factors, we perform genome wide translation profiling. We used polysome recruitment profiling to assess which transcripts are subject to regulation of translation initiation, and we use ribosome profiling to assess on which start codons ribosomes associate to start translation. These studies are ongoing.

Among the proteins whose translation is tightly controlled are Use1 (Unusual SNARE protein in the ER 1), Igbp1 (Immunoglobulin binding protein 1, also known as the alpha4 subunit of protein phosphatase 2a (Pp2a)), Nme2 (Never in mitosis 2).

We thought that these transcripts were also affected in Diamond Blackfan Anemia (DBA), a disease with congenital mutations in ribosomal proteins. This was not the case. Instead we found impaired translation of transcripts translated from an internal ribosomal entry site (IRES). Among them are Bag1 (Bcl2 athanogene 1) and Csde1 (cold shock domain protein e1) that are 20 and 200-fold upregulated, respectively, when hematopoietic progenitors differentiate to erythroblasts. Translation of Bag1 and Csde1 is also impaired in erythroblasts cultured from blood of DBA patients. Mice lacking Bag1 die before birth due to a lack of mature erythrocytes. Lack of Bag1 increases the phosphorylation of translation initiation factor 2, which may particularly affect the translation of transcripts with upstream open reading frames. Knock-down of Csde1 severely impairs erythroid proliferation and differentiation. Csde1 is an IRES transactivating factor. We are currently identifying the transcripts that depend on Csde1 for translation to identify the mechanisms that are affected.

Key Publications

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Last edited on: 16 April 2013